(The directional light lits the side shown at the right side of the picture.)
I tried changing shaders, but that just makes the bright side fully dark.
I tried changing Ambient Occlusion but that make the normal side fully dark, and the bright side normal.
I use the "Green Forest" (free) asset from the Unity Store.
Currently it uses the "Hidden/Nature/Tree Creator Leaves Optimized" shader.
Some types of trees got fixed by turning off AO, and setting shadow strength to 0 both at the shader and at the Tree component, but for example the tree on the picture can't be fixed for some reason.
One type got fixed by setting its shader to "Tree Creator Leaves Fast". But that way shadows "float" around the leaves.
Why does this happen?